ABSTRACTThe present study examined the changes in protein expression in Spirulina platensis upon exposure to high temperature, with the changes in expression analyzed at the subcellular level. In addition, the transcriptional expression level of some differentially expressed proteins, the expression pattern clustering, and the protein-protein interaction network were analyzed. The results obtained from differential expression analysis revealed up-regulation of proteins involved in two-component response systems, DNA damage and repair systems, molecular chaperones, known stress-related proteins, and proteins involved in other biological processes, such as capsule formation and unsaturated fatty acid biosynthesis. The clustering of all differentially expressed proteins in the three cellular compartments showed: (i) the majority of the proteins in all fractions were sustained tolerance proteins, suggesting the roles of these proteins in the tolerance to high temperature stress, (ii) the level of resistance proteins in the photosynthetic membrane was 2-fold higher than the level in two other fractions, correlating with the rapid inactivation of the photosynthetic system in response to high temperature. Subcellular communication among the three cellular compartments via protein-protein interactions was clearly shown by the PPI network analysis. Furthermore, this analysis also showed a connection between temperature stress and nitrogen and ammonia assimilation.

Figure 5: RT-PCR analysis of the transcriptional level of a differentially expressed protein, AP07830020 - Molecular chaperone DnaK (spot no. 912_TM). (Note: Some of the standard deviation values are too small to be seen as error bars.)

Mentions:
RT-PCR was used to analyze the transcriptional expression levels of some differentially expressed proteins (Fig. 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10) [see fig S5; Additional file 2]. The transcriptional expression patterns of DNA gyrase and chromosome segregation ATPase from the soluble fraction, and ABC transporter, S-adenosyl-L-homocysteine hydrolase and Δ9 desaturase from the thylakoid membrane were well correlated with the protein expression patterns. This correlation suggests that these proteins are likely regulated at the transcriptional level. Interestingly, the Δ9 desaturase gene, the first gene in the fatty acid desaturation process of Spirulina, was previously reported to be temperature-independent [9]. However, an earlier study by our group using Northern blot analysis [see fig S4; Additional file 2] demonstrates that this gene is indeed temperature-dependent, in agreement with the results obtained in the present study.

Figure 5: RT-PCR analysis of the transcriptional level of a differentially expressed protein, AP07830020 - Molecular chaperone DnaK (spot no. 912_TM). (Note: Some of the standard deviation values are too small to be seen as error bars.)

Mentions:
RT-PCR was used to analyze the transcriptional expression levels of some differentially expressed proteins (Fig. 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10) [see fig S5; Additional file 2]. The transcriptional expression patterns of DNA gyrase and chromosome segregation ATPase from the soluble fraction, and ABC transporter, S-adenosyl-L-homocysteine hydrolase and Δ9 desaturase from the thylakoid membrane were well correlated with the protein expression patterns. This correlation suggests that these proteins are likely regulated at the transcriptional level. Interestingly, the Δ9 desaturase gene, the first gene in the fatty acid desaturation process of Spirulina, was previously reported to be temperature-independent [9]. However, an earlier study by our group using Northern blot analysis [see fig S4; Additional file 2] demonstrates that this gene is indeed temperature-dependent, in agreement with the results obtained in the present study.

Bottom Line:
In addition, the transcriptional expression level of some differentially expressed proteins, the expression pattern clustering, and the protein-protein interaction network were analyzed.The results obtained from differential expression analysis revealed up-regulation of proteins involved in two-component response systems, DNA damage and repair systems, molecular chaperones, known stress-related proteins, and proteins involved in other biological processes, such as capsule formation and unsaturated fatty acid biosynthesis.Furthermore, this analysis also showed a connection between temperature stress and nitrogen and ammonia assimilation.

ABSTRACTThe present study examined the changes in protein expression in Spirulina platensis upon exposure to high temperature, with the changes in expression analyzed at the subcellular level. In addition, the transcriptional expression level of some differentially expressed proteins, the expression pattern clustering, and the protein-protein interaction network were analyzed. The results obtained from differential expression analysis revealed up-regulation of proteins involved in two-component response systems, DNA damage and repair systems, molecular chaperones, known stress-related proteins, and proteins involved in other biological processes, such as capsule formation and unsaturated fatty acid biosynthesis. The clustering of all differentially expressed proteins in the three cellular compartments showed: (i) the majority of the proteins in all fractions were sustained tolerance proteins, suggesting the roles of these proteins in the tolerance to high temperature stress, (ii) the level of resistance proteins in the photosynthetic membrane was 2-fold higher than the level in two other fractions, correlating with the rapid inactivation of the photosynthetic system in response to high temperature. Subcellular communication among the three cellular compartments via protein-protein interactions was clearly shown by the PPI network analysis. Furthermore, this analysis also showed a connection between temperature stress and nitrogen and ammonia assimilation.